Process for the production of polymer materials

ABSTRACT

A high modulus polymer material is produced by subjecting a crystallisable polymer to a thermal treatment under conditions such that the possibility that a given molecular chain is incorporated in more than one crystal lamella is substantially reduced and then attenuating the polymer at an imposed rate and temperature whereby substantially complete alignment of its molecules may be obtained.

This is a continuation of application Ser. No. 782,225, filed Mar. 28,1977 now abandoned, which is a continuation of Ser. No. 562,043 filedMar. 26, 1975, now abandoned, and a continuation in part of Ser. No.508,879, filed Sept. 24, 1974, now abandoned.

This invention relates to certain new polymer materials, and processesfor their production.

U.K. Patent Application Ser. No. 10746/73 describes shaped articles, andparticularly filaments films, and fibres of high density polyethylene,having a Young's modulus (dead load creep) of greater than 3×10¹⁰ N/m².According to U.K. Patent Application Ser. No. 10746/73 polyethylenearticles of high modulus are obtained from polymers having a weightaverage molecular weight (Mw) of less than 200,000 and a number averagemolecular weight (Mn) of less than 20,000 and a ratio of Mw/_(Mn) ofless than 8 where Mn is greater than 10⁴, and of less than 20 where Mnis less than 10⁴ by cooling the polymer from a temperature at or closeto its melting point at a rate of 1° to 15° per minute followed bydrawing the cooled polymer.

According to the present invention, it has now been found that a highmodulus polymer material may be produced by subjecting a crystallisablepolymer to a thermal treatment under conditions such that thepossibility that a given molecular chain is incorporated in more thanone crystal lamella is substantially reduced and then attenuating thepolymer at an imposed rate and temperature whereby substantiallycomplete aligment of its molecules may be obtained.

The present invention provides a process for the production of a highmodulus polymer material which comprises subjecting a crystallisablepolymer having a weight average molecular weight of less than 300,000and preferably less than 200,000 to a thermal treatment such that thepossibility that a given molecular chain is incorporated in more thanone crystal lamella is substantially reduced, and attenuating thepolymer at a temperature and a rate such that the deformation ratio isat least 15.

In this specification a crystallisable polymer is defined as one that iscapable of forming a crystalline or semi-crystalline structure oncooling from the melt. The invention may be applied to a range ofcrystallisable polymers, but is particularly applicable to vinylpolymers, and more especially to those vinyl polymers that crystallisein a folded chain form, for example linear vinyl hydrocarbon polymerssuch as polyethylene, polypropylene and ethylene/propylene blockcopolymers. The invention may also be applied to other essentiallylinear organic polymers such as polyethylene oxide, polyoxymethylene andpolyacetaldehyde, and fluorinated polymers such aspolytetrafluoroethylene and polychlortrifluorethylene. Particularly goodresults have been obtained with high density polyethylene which in thisspecification is defined as a substantially linear homopolymer ofethylene or a copolymer of ethylene containing at least 95% by weight ofethylene, having a density of from 0.91 to 1.0 gms/cm³ as measured bythe method of British Standard Specification No. 2782 (1970) method 509Bon a sample prepared according to British Standard Specification No.3412 (1966) Appendix A and annealed according to British StandardSpecification No. 3412 (1966) Appendix B(1), such as for example thatproduced by polymerising ethylene in the presence of a transition metalcatalyst.

The crystallisable polymer should have a reasonably high weight averagemolecular weight in order that the shaped article after attenuation willhave acceptable physical properties, such as tenacity and extensibilityat break. However a high concentration of long molecules increases thechance that a given molecular chain before attenuation will becomeincorporated in more than one crystal lamella. Henceforth in thisspecification such molecular chains will be termed "inter-lamellarmolecular chains". Although the invention is not limited to anyparticular theory it is believed that an excessive number ofinter-lamellar molecular chains reduces the degree of molecularorientation and alignment obtainable upon attenuation due to an increasein the number of permanent physical entanglements, and consequentlyprevents the attainment of the optimum physical properties.

Preferably the weight average molecular weight (Mw) of the polymer isfrom 50,000 to 250,000, more preferably 50,000 to 150,000 and the numberaverage molecular weight (Mn) is preferably from 5,000 to 25,000 morepreferably 5,000 to 15,000. It will usually be advantageous to avoidlarge values of the ratio of Mw to Mn in order that there is a morehomogeneous deformation at a molecular level during the attenuationprocess. Preferably the ratio of Mw to Mn is less than 30. Particularlygood results have been obtained using polymers having a relativelynarrow molecular weight distribution, such that for Mn greater than 10⁴,Mw/Mn is less than 10 and preferably less than 8 and most preferablyless than 6, and for Mn less than 10⁴, Mw/Mn is less than 25 and mostpreferably less than 15. The molecular weights quoted in thisspecification are those measured by the gel permeation chromatographymethod.

The thermal treatment may have the effect of reducing the probabilitythat an excessive number of molecular chains are incorporated in morethan one lamella for example by achieving a molecular weightfractionation in the sense that a substantial fraction of the moleculesof intermediate molecular weight are allowed to crystallise in discretevery regularly folded chain lamellae whilst a smaller number of bothvery high and very low molecular weight molecules separate and in a fewcases interconnect the crystalline regions. This effect may be obtainedin three ways:

(1) Cooling the polymer from a temperature at or above its melting pointat a predetermined rate to ambient temperature so that the desiredcrystal structure is obtained. The cooling rate used is dependent uponthe molecular weight characteristics of the polymer. Usually it isnecessary to cool the polymer at an imposed rate of less than 40° C. perminute and preferably less than 20° C. per minute. Most preferably thecooling rate is less than 10° C. per minute.

(2) Cooling the polymer from a temperature at or above its melting pointat a predetermined rate to a temperature below its crystallisationtemperature and then quenching the polymer to ambient temperature. Thecooling rate is preferably from 1° to 15° C. per minute, and mostpreferably from 2° to 10° C. per minute. Preferably the polymer isquenched after reaching a temperature of from 5° to 20° C. below itscrystallisation temperature. Quenching should preferably be at a rate ofless than 100,000° C. per minute.

(3) Rapidly cooling or quenching the polymer from a temperature at orabove its melting point to a temperature close to or at itscrystallisation temperature and maintaining the polymer at thattemperature for a period of time sufficient to allow crystallisation tooccur.

Preferably the polymer is held at a temperature which is within 15° C.of the crystallisation temperature for a period of time of from 0.5 to10 minutes. Subsequently, the polymer is preferably quenched to ambienttemperature.

Optical micrographs of samples produced according to methods (1), (2)and (3) above show that polymers having the specified molecular weightcharacteristics produce a macrostructure comprising uniformly orienteddomains of varying size which occupy the whole of the polymer. For highdensity polyethylene these domains can be up to 15μ in size.

The choice of conditions used in methods (1), (2) and (3) will dependupon the molecular weight characteristics of the polymer. In general,however, extremely slow cooling rates (less than 1° C./minute) do notproduce a crystal structure suitable for attenuation if the polymer hasa particularly narrow molecular weight distribution. Also cooling ratesgreatly in excess of 40° C./minute for methods (1) and (2) and excessiveperiods of retention at the crystallisation temperature for method (3)have also been found to be deleterious.

FIGS. 1(a), 1(b) and 1(c) illustrate, in the case of high densitypolyethylene, respectively, crystal structures produced by methods (1),(2) and (3) of the present invention.

An alternative method of producing a crystal structure in which thepossibility that a given molecular chain is incorporated in more thanone crystal lamella is substantially reduced, comprises cooling thepolymer very rapidly from a temperature at or above its melting point toa temperature well below its crystallisation temperature to achieve acomparatively low crystallinity. This method, which will be termedmethod (4) greatly reduces the size of the spherulites and produces astructure comprising crystallites surrounded by large amorphous regions,thereby reducing the number of inter-lamellar molecular chains.Preferably the cooling rate is in excess of 1,000° C./minute, mostpreferably in excess of 5,000° C./minute through the crystallisationrange, and the polymer is cooled to ambient temperature or below.Depending upon the molecular weight characteristics of the polymer itmay be found advantageous to reheat the cooled polymer to increase thesize of the crystalline regions before attenuation.

Optical micrographs of samples produced by method (4) show moreconventional clearly banded spherulitic structures, but may bedistinguished by the small size of the spherulites. FIG. 1(d)illustrates, in the case of high density polyethylene, a crystalstructure produced by method (4) of the present invention.

The structures formed in the different methods of thermal treatment donot deform equally under given conditions. For each structure there willbe an optimum attenuation procedure. Attenuation may be undesirablylimited if there is appreciable molecular orientation in the undrawnmaterial.

The crystallisation of the polymers has been extensively studied andbooks such as Crystallisation of Polymers by L. Mandelkern published byMcGraw-Hill 1964 (Chapter 8--Crystallisation Kinetics and Mechanism)review the subject. By observing changes in properties such as densityor specific volume, it has been shown that crystallisation occurs instages. There may be a time delay before crystallisation is observed,but as soon as it is observed the process proceeds at an acceleratingrate which is almost autocatalytic in nature. Finally, apseudo-equilibrium level of crystallisation is reached, after which asmall but definite amount of crystallisation at very slow rates persistsfor a long period of time. The crystallisation process is a continuousone with no sudden changes or discernible discontinuities observed inthe plot of degree of crystalliation against time which is sigmoidal inshape. The rapid crystallisation is referred to as initialcrystallisation, and the slower crystallisation stage is referred to assecondary crystallisation. It is believed that secondary crystalliationis disadvantageous in obtaining high moduli, and whereas some polymersmay tolerate a degree of secondary crystalliation and still giveacceptable properties on attenuation, it is found that the highestmoduli are obtained when secondary crystallisation has not been allowedto become the dominant process. At least for methods (1), (2) and (3) itis usually found to be advantageous to allow crystalliation to proceeduntil the rapid initial crystalliation is substantially complete. Theprogress of crystallisation can be followed by measuring the density ofthe polymer.

In methods (1), (2) and (3), for a given method of thermal treatment anda given polymer, the maximum attenuation achievable (hence the maximummodulus obtainable) increases with increasing density of the polymeruntil an optimum density is reached, above which the maximum attenuationobtainable may decrease. By attenuating samples of different densitiesunder the same conditions, it is thus possible to determine the optimumdensity of the polymer for a given set of attenuation conditions.

After thermal treatment the polymer is then attenuated at a temperatureand a rate such that the deformation ratio is at least 15, andpreferably at least 20. It is believed that the high degree ofattenuation required to obtain a high modulus is achieved by ahomogeneous extension of the polymer, corresponding at the molecularlevel to the unfolding of the molecules in the crystal lamellae andtheir subsequent orientation.

A particularly preferred attenuation process comprises drawing thepolymer to a high draw ratio at a speed and at a temperature such thatthe tension of drawing is less than the tensile strength of the polymer,but sufficient to produce alignment of the molecules by inducing therequired plastic deformation over and above any extension which may beproduced by flow drawing. Preferably the draw ratio is at least 20.

The optimum drawing conditions depend to some extent upon the nature ofthe polymer and its previous thermal history. As a general rule thepolymers are preferably drawn relatively slowly for example betweenrelatively movable clamping means, at speeds in excess of 1 cm perminute, usually around 10 to 20 cm per minute and at a temperature atleast 40° C. below the melting point of the polymer or on a draw frameat speeds of from 30 to 150 cms per minute at higher temperatures offrom 5° to 20° C. below the melting point.

It has been found that the physical properties of the polymer materialcan sometimes be further improved by carrying out the drawing process inincremental stages, allowing the polymer to rest between successivestages.

It is preferred to carry out the drawing process upon a polymer having arelatively small cross-section and the invention is particularlysuitable for the production of fibres and films. In particularcontinuous filaments may be produced by melt spinning and drawing on adraw frame. For convenience the diameter of the fibre, or the thicknessof the film, before drawing is preferably less than 1 mm.

In this specification the deformation ratio or draw ratio is definedeither as the ratio of the final length to the initial length or as theratio of the cross-sectional areas before and after drawing.

The process of the invention is capable, for example, of producing apolyethylene polymer material having a Young's modulus as hereinafterdefined well in excess of 3×10¹⁰ N/m² and in some cases at least 6×10¹⁰N/m². The Young's modulus of a polymer material depends partly upon themethod of measurement, and therefore in this specification Young'smodulus is defined as being the modulus measured at 21° by adead-loading creep experiment, as described by Gupta & Ward in J.Macromo. Sci. Phys. B1 373 (1967), taking the 10 second response at astrain of 0.1%. It is found that, in accordance with the process of theinvention, substantially complete alignment of the polymer molecules canbe obtained by plastic deformation. The molecular orientation will inmost cases be uniaxial, although it is also possible with an appropriatedrawing process, to produce biaxially oriented polymer materials. Thepresence of substantially complete orientation may be determined byphysical measurements, such as for example, X-ray diffractionmeasurements, or nuclear magnetic resonance studies.

By the process of the present invention polyethylene materials with amodulus above 5×10¹⁰ N/m² have been produced. A theoretical estimate forthe Young's modulus of polyethylene is 24×10¹⁰ N/m² and it can thus beseen that the polymer materials of the invention have a modulus whichapproaches quite closely to this figure.

Polymer materials according to the present invention can be produced inthe form of coherent unitary structures.

The invention is illustrated by the following Examples:

EXAMPLE 1

Isotropic filaments of 0.06-0.07 cm diameter are obtained by meltingspinning high density polyethylenes (described hereinafter) at 190° C.through a 0.1 diameter die. The filaments are wound up on a cylinder of5.5 cm diameter rotating at a speed of 2.3 revs/min. The cooling rate ofthe polymer is arranged to be 5° C. per minute and the structureproduced when the temperature of the polymer reaches 115° C. ispreserved by rapid cooling. Samples 3-4 cm long are subsequently drawnon an Instron tensile testing machine at 72° C. with a cross-head speedof 20 cm/min for 30-45 secs. The draw ratio is determined from thevariation in cross-section of the filament.

This process is undertaken with two polymers from the commercial rangeof BP high density polyethylene; 075-60 grade with a melt flow index of8.0 measured at 190° C. with a load of 2.14 kg, M_(n) of 14,450, andM_(w) of 69,100, and for comparison, Rigidex 9, with a melt flow indexof 0.9, M_(n) of 6,060 and M_(w) of 126,600. The 10 sec Young's modulusis measured at room temperature (21° C.). The 075-60 grade had a narrowmolecular weight distribution, (Mw/Mn)=4.8, and gives a drawn producthaving a draw ratio of 20 and a Young's modulus of 4.0×10¹⁰ N/m². Incontrast, the Rigidex 9 has a broader molecular weight distribution,(Mw/Mn)=20.9 as well as higher Mw value, and consequently gives a drawnproduct having a considerably lower modulus. Continuous filaments of theabove materials may be drawn on a draw frame with similar results.

EXAMPLE 2

0.05-0.07 cm thick sheets are obtained by compression moulding highdensity polyethylene pellets at 160° C. between two copper plates. Thesesheets are then removed from the press and slowly cooled at a rate of7°-9° C./min to a temperature of 100° C. (measured on the surface of thecopper plate) and then quenched in cold water. Rectangular samples 2 cmlong and 0.5 cm wide are drawn on an Instron tensile testing machine at75° C. at a cross-head speed of 10 cm/min for 70-90 secs. The draw ratiois measured from marks on the surface of the undrawn samples spaced atintervals of 0.2 or 0.1 cm.

The polymers investigated are two different grades from the commercialrange of BP high density polyethylene, Rigidex 50, with a melt flowindex of 5.5 Mn of 6180 and Mw of 101,450, and 140-160 grade with a meltflow index of 12, Mn of 13,350 and Mw of 67,800. A maximum draw ratio of30 is measured for the Rigidex 50, and a maximum draw ratio of 37-38 forthe 140-60 grade.

The 10 sec Young's modulus for representative samples is measured atroom temperature and the results given in the following Table 1.

                  TABLE 1                                                         ______________________________________                                                                   10 sec Young's modulus                                                        (N/m.sup.2 × 10.sup.-10) strain                      Melt               0.1 × 10.sup.-2 after thermal                        Flow               treatment and drawing                              Materials                                                                             Index   Draw Ratio Room temperature                                   ______________________________________                                        Ridigex 50                                                                            5.5     27         5.7                                                  "     "       30         6.8                                                140-160 12.0    28         5.7                                                ______________________________________                                    

Examples 3 to 5 illustrate that the maximum draw ratio obtainable occursat an optimum density, and that the optimum density is a function of theconditions of the thermal treatment.

EXAMPLE 3

A film of high density polyethylene (Rigidex 25--a product of BPLtd.--having Mw of 98,800 and Mn 12,950) was formed by compressionmoulding at 160° C. the polymer between two copper sheets of 0.5 mmthickness. The plates were then removed from the press and wrapped in athick layer of cotton wool whereby the polymer, as shown by athermocouple, cooled at a rate of 5° C. per minute. On reaching 120° C.the plates were dropped into a bath of glycerol maintained at 120° C.and kept there for a period of time varying from 0 (no bath) to 10minutes. The density of the film was measured using a density column.Dumbell samples of the film were drawn for 60 seconds on an InstronTensile Testing Machine at a temperature of 75° C. and a crosshead speedof 10 cm per minute. The undrawn sample was marked at intervals of 0.2cms or 0.1 cms and the draw ratio occurring during drawing wasdetermined by the increase in length of the drawn sample. Table 2 showsthe effects of dwell time at 120° C. on density and the maximum drawratio.

EXAMPLE 4

Example 3 was repeated except that the plates on removal from the presswere immediately immersed in the glycerol bath, the polymer therebycooling from 160° C. to 120° C. at a rate of 40° C. per minute. Table 2shows the effect of density on draw ratio.

EXAMPLE 5

Example 3 was repeated except that the polymer was sandwiched betweensheets of aluminium foil and the whole sandwiched between copper plateswhich were immediately removed before the aluminium plates and film weredropped into the glycerol bath. The rate of cooling in this case was400° C. per minute, and the effect of dwell time at 120° C. on densityand maximum draw ratio obtainable is given in Table 2.

                  TABLE 2                                                         ______________________________________                                               Cooling    Time at                                                            Rate       120° C.                                                                          Density Maximum                                   Example                                                                              (°C. per min)                                                                     (mins)    (tonne/m.sup.3)                                                                       Draw Ratio                                ______________________________________                                                          0         0.9628  19.5                                      3       5         1         0.9646  16.8                                                        2         0.9648  18.2                                                        3         0.9646  16                                                          0         0.9508  10.3                                      4      40         1         0.9597  12                                                          2         0.9628  16                                                          9         0.9656  15                                                          0.5       0.9546  17.5                                      5      400        1         0.9606  20                                                          2         0.9618  18.3                                                        10        0.9646  16.5                                      ______________________________________                                    

EXAMPLE 6

High density polyethylene (Rigidex 140-60--a product of BP Ltd.--havingMw of 67,800 and Mn 13,350) was extruded at 180° C. through a spinnerethaving an orifice of 0.9 mm to give a filament which was passed througha bath of glycerol maintained at 120° C. before being wound up, theposition of the bath below the spinneret and the dwell time of thefilament in the bath being varied. The temperature of the filamententering the bath was about 135° C. The filament was drawn under theconditions as described in Example 3. Further details of the spinningand drawing conditions, and of the properties of the drawn filament aregiven in Table 3, the modulus being measured at 21° C. by a dead loadcreep experiment as described by Gupta & Ward in J. Macromol. Sci. Phys.B1, 373 (1967).

                                      TABLE 3                                     __________________________________________________________________________                Wind                                                                              Distance                Creep                                 Through-                                                                             Extrusion                                                                          up  of bath                                                                            Bath                                                                              Bath                                                                              Density                                                                            Maximum                                                                             modulus                               put    temp.                                                                              speed                                                                             from temp.                                                                             lgth                                                                              (tonne/                                                                            draw  (× 10.sub.2.sup.-8              (g.p.m.)                                                                             (°C.)                                                                       (fpm)                                                                             spinneret                                                                          (°C.)                                                                      cms m.sup.3)                                                                           ratio N/m                                   __________________________________________________________________________    a 0.3  180  5   None None                                                                              None                                                                              0.9554                                                                              14   --                                    b --   180  5   8    120 150 0.9617                                                                             33.5  500                                   c 0.71 180  5   12.5 120 150 0.9626                                                                             33.5  600                                   d 0.54 180  5   12.5 120  50 0.9620                                                                             54    720                                   __________________________________________________________________________

The spun filament of Example 6 when cross-sectioned and examined under apolarising microscope exhibited uniformly orientated regions evenlyscattered throughout the material, the regions being suggestive of theinitial sheaves in spherulitic growth.

EXAMPLE 7

Example 6 was repeated except that the spun filament was wound up at aspeed of 150 cm per minute and the temperature of the bath was variedfrom 60° to 125° C. The temperature of the filament on entering the bathwas measured using an infra-red pyrometer. Details of the properties ofthe spun filament are given in Table 4.

EXAMPLE 8

High density polyethylene (Rigidex 140-60) was spun into a singlefilament and quenched using the same apparatus as that used for Example6. The conditions used were as follows:

    ______________________________________                                        Throughput              0.3 g.p. min.                                         Extrusion temperature   180° C.                                        Wind-up speed           5 f.p.m.                                              Quench distance from spinneret                                                                        7.5 cm                                                Quench temperature      120° C.                                        Quench length           50 cm                                                 ______________________________________                                    

The resulting spun yarn was drawn continuously on a draw frame over apin maintained at 130° C. at a draw ratio of 23.8 and a draw speed of 1f.p.m. The drawn filament has a tenacity of 6.7 g.p.d' tex and extensionto break of 2.9%, and a creep modulus of 450×10⁸ N/m².

                                      TABLE 4                                     __________________________________________________________________________              Dwell                                                               Length of time                                                                bath (cm) (sec)                                                                     Fila-                                                                             Fila-                                                                     ment                                                                              ment 12.5cm/5s                                                                            25cm/10s                                                                              50cm/20s                                                                              100cm/40s                                                                             150cm/60s                                                                             300cm/120s              Bath  Dia-                                                                              Temp. at                                                                              Den-    Den-    Den-    Den-     Den-   Den-                Temp  meter                                                                             Entry                                                                              Max                                                                              sity                                                                              Max sity                                                                              Max sity                                                                              Max sity                                                                              Max sity                                                                              Max sity                (°C.)                                                                        (mm)                                                                              (°C.)                                                                       DR g/cm.sup. 3                                                                       DR  g/cm.sup.3                                                                        DR  g/cm.sup.3                                                                        DR  g/cm.sup.3                                                                        DR  g/cm.sup.3                                                                        DR  g/cm.sup.3          __________________________________________________________________________    a 125 0.65                                                                              120  -- --  --  --  Broke                                                                             0.9619                                                                            --  --  Broke                                                                             0.9640                                                                            --  --                  b 120 0.45                                                                              120  -- --  --  --  Broke                                                                             0.9612                                                                            --  --  11.5                                                                              0.9618                                                                            --  --                  c 120 0.65                                                                              120  19 0.9604                                                                            25-30                                                                             0.9610                                                                            17-22                                                                             --  Broke                                                                             0.9610                                                                            --  --  Broke                                                                             0.9620              d 120 0.65                                                                              130  17 0.9604                                                                            13-22                                                                             0.9607                                                                            27-31                                                                             0.9612                                                                            16  --  Broke                                                                             0.9618                                                                            --  --                  e 120 0.65                                                                              135  28 0.9603                                                                            --  --  16  0.9624                                                                            --  --  --  --  --  --                  f 120 0.80                                                                              120  -- --  --  --  Broke                                                                             0.9624                                                                            --  --  Broke                                                                             0.9628                                                                            --  --                  g 110 0.65                                                                              120  -- --  --  --  17  0.9617                                                                            --  --  16  0.9617                                                                            --  --                  h 100 0.65                                                                              120  -- --  --  --  16  0.9612                                                                            --  --  25  0.9610                                                                            --  --                  i  90 0.65                                                                              130  -- --  --  --  Broke                                                                             --  --  --  23  --  --  --                  j  90 0.65                                                                              120  -- --  --  --  Broke                                                                             --  --  --  16  --  --  --                  k  60 0.65                                                                              120  -- --  --  --  Broke                                                                             --  --  --  Broke                                                                             --  --  --                  __________________________________________________________________________

EXAMPLE 9

Samples of Rigidex 50 and 140-60 grade were compression moulded betweenmetal plates at a temperature of 160° C. and subsequently cooled down toroom temperature at a non-linear cooling rate <0.8° C./min. 2 cm longand 0.5 cm wide dumbell samples were then drawn in an Instron at 75° C.Details of the experiment and results are shown in Table 5.

The remarkable difference in drawing behaviour for samples of identicalinitial crystallinity is related to the width of the molecular weightdistribution and hence the molecular weight of the molecules in thenon-crystalline phase.

Optical micrographs of isotropic samples of Rigidex 50 prepared in thisway show regions of uniform orientation whilst the isotropic samples of140-60 polymer exhibit before drawing a clear spherulitic morphology.

                  TABLE 5                                                         ______________________________________                                                Density of                   Density of                                       isotropic Cross-head         drawn                                            sheet     speed      Draw ratio                                                                            samples                                  Polymer (g/cm.sup.3)                                                                            (cm/min)   (λ)                                                                            (g/cm.sup.3)                             ______________________________________                                        Rigidex 50                                                                            0.973     10         ˜25                                                                             0.963                                    "       0.973      5         ˜25                                                                             0.963                                    140-60  0.973     10         Break   --                                       "       0.973      5         Break   --                                       ______________________________________                                    

EXAMPLE 10

Samples of Rigidex 50, 140-60 grade BXP 10 (a polyethylene of Mn 168,000and Mw 93,800) and Rigidex 9 were compression moulded at 160° C. betweenmetal plates and then quenched in water at room temperature. High drawratics were obtained by drawing 2 cm long and 0.5 cm wide dumbellsamples at 75° C. in an Instron for different times. Experimentaldetails and results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                  Cross-head                                                                    speed      Drawing time                                                                             Draw ratio                                    Polymer   (cm/min)   (sec)      (λ)                                    ______________________________________                                        Rigidex 50                                                                              10         160        20                                              "       10          290*       32*                                          140-60    10         150        30                                            BXP-10    10         160        17                                            BXP-10    10          250*       31*                                          Rigidex 9 10         215        23                                            ______________________________________                                         *These samples due to the experimental limitations have been obtained by      redrawing part of the samples originally drawn for 160 seconds under the      assumption of a continuous deformation process.                          

EXAMPLE 11

Polypropylene samples of different molecular weight were spun at 185° C.through a die of 0.2 cm diameter using a ram speed of 0.6 cm per minuteand a winding up speed of 110 cm per minute in air. The take up spoolwas at about 3 cm from the die. The filaments were drawn on a draw frameat a take up speed of about 130 cm per minute and the multi-stageprocess is described in Table 7:

                  TABLE 7                                                         ______________________________________                                                  Pin temperature                                                     Stage     in °C.                                                                             Imposed Draw Ratio                                      ______________________________________                                        1st       120           7:1                                                   2nd       110         1.5:1                                                   3rd       100         1.5:1                                                   4th        90         1.5:1                                                   ______________________________________                                    

Molecular weight characteristics, draw ratios and creep moduli for thetwo materials examined are shown in Table 8:

                  TABLE 8                                                         ______________________________________                                                   Machine      Modulus     Modulus                                   Material   Draw Ratio   N/m.sup.2 × 10.sup.-10                                                              g.p. d'tex                                ______________________________________                                        H.F. 56                                                                       --Mw = 260,000                                                                           23           0.8         90                                        --Mn = 39,000                                                                 Degraded H.F. 56                                                              --Mw = 134,000                                                                           23           1.4-1.6     157-179                                   --Mn = 30,000                                                                 ______________________________________                                    

EXAMPLE 12

Isotropic filaments of 0.04-0.06 cm diameter are obtained bymelt-spinning polyoxymethylene (Delrin 500--a product of Du Pont deNemours having M_(n) of 45,000 and M_(w) /M_(n) slightly greater than 2)at 3/4180° C. through a 0.2 cm diameter die in air using a ram speed ofapproximately 0.6 cm/min and a winding-up speed of 36 cm/min. Thetake-up spool was at about 7 cm from the die.

The filaments were drawn in two stages on a draw-frame at a take-upspeed of about 50 cm/min. Details of the process are given in Table 9.

                  TABLE 9                                                         ______________________________________                                              Pin Temperature                                                                              Imposed Draw                                                                              Total Draw                                   Stage in °C.  Ratio       Ratio*                                       ______________________________________                                        1st   ˜140° C.                                                                        7.1         7.4:1                                        2nd   ˜140°  C.                                                                       2.8:1        20:1                                        ______________________________________                                         *As measured from the displacement of marks on the sample surface.       

The 10 sec Young's moduli, as from a dead loading creep experiment, atdifferent temperatures are shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                        Young's Modulus                                               Temperature (°C.)                                                                      (N/m.sup.2 × 10.sup.-10)                                ______________________________________                                        +20             4.9                                                           -50             5.9                                                            -150           8.1                                                           ______________________________________                                    

We claim:
 1. A process for the production of a high modulus polymermaterial which comprises quenching a crystallizable polymer selectedfrom the group consisting of high density polyethylene, ethylenecopolymers containing at least 95% by weight of ethylene, andpolyoxymethylene having a weight average molecular weight (Mw) of lessthan 300,000 and a ratio of Mw to number average molecular weight (Mn)less than 30 from a temperature at or above its melting point to atemperature at or close to its crystallization temperature; maintainingthe polymer at the temperature for a time sufficient to allowcrystallization to occur; and then attenuating the polymer at atemperature below its melting point at a rate such that the deformationratio (the ratio of the final length to the initial length) is at least15.
 2. A process according to claim 1, in which the crystallizablepolymer has Mw < 200,000.
 3. A process according to claim 1, in whichthe crystallizable polymer is high density polyethylene.
 4. A processaccording to claim 1, in which Mw is from 50,000 to 250,000.
 5. Aprocess according to claim 4, in which Mw is from 50,000 to 150,000. 6.A process according to claim 3, in which Mn is from 5,000 to 25,000. 7.A process according to claim 6, in which Mn is from 5,000 to 15,000. 8.A process according to claim 1, in which for Mn greater than 10⁴, Mw/Mnis less than 10 and for Mn less than 10⁴, Mw/Mn is less than
 25. 9. Aprocess according to claim 1, in which the deformation ratio is at least20.
 10. A process according to claim 1, in which the polymer isattenuated on a draw frame at a speed of from 30 to 150 cm per minute ata temperature of from 5° to 20° C. below the melting point of thepolymer.
 11. A process according to claim 1, in which the attenuation iscarried out in incremental stages, allowing the polymer to rest betweensuccessive stages.
 12. A process according to claim 1, in which there isproduced a fiber or film.
 13. A process according to claim 12, in whichthe diameter of the fiber or the thickness of the film beforeattenuation is less than 1 mm.
 14. A process according to claim 1, inwhich the crystallizable polymer is polyoxymethylene.
 15. A processaccording to claim 14, wherein attenuation is effected at a temperatureof about 140° C.